A switched-mode power supply (SMPS) typically includes a power stage circuit and a controller. The controller may be used to regulate the conduction and shutdown times of the switches in the power stage circuit. This may be done regardless of variation in input voltage, inside parameters, and load, in order to keep the output voltage or output current of the SMPS substantially constant. Therefore, it is important to choose a proper controlling method, and to design a proper controller for the SMPS, as different performance may result from different controlling methods and/or controllers.